Molecular Epidemiology of Rabies Viruses Circulating in Two Rabies Endemic Provinces of Laos, 2011–2012: Regional Diversity in Southeast Asia

BackgroundAlthough rabies is endemic in Laos, genetic characterization of the viruses in this country is limited. There are growing concerns that development in the region may have increased transport of dog through Laos for regional dog meat consumption, and that this may cause spillover of the viruses from dogs brought here from other countries. This study was therefore undertaken to evaluate the current rabies situation and the genetic characteristics of rabies viruses currently circulating in Laos.MethodsWe determined the rate of rabies-positive samples by analyzing data from animal samples submitted to the Lao Ministry of Agriculture and Forestry’s National Animal Health Centre rabies laboratory from 2004 through 2011. Twenty-three rabies-positive samples were used for viral genetic characterization. Full genome sequencing was performed on two rabies viruses.ResultsRabies-positive samples increased substantially from 40.5% in 2004 to 60.2% in 2009 and continued at this level during the study period. More than 99% of the samples were from dogs, followed by cats and monkeys. Phylogenetic analyses showed that three rabies virus lineages belonging to the Southeast Asian cluster are currently circulating in Laos; these are closely related to viruses from Thailand, Cambodia and Vietnam. Lineages of the circulating Laos rabies viruses diverged from common ancestors as recently as 44.2 years and as much as 55.3 years ago, indicating periodic virus invasions.ConclusionThere is an increasing trend of rabies in Laotian animals. Similar to other rabies-endemic countries, dogs are the main viral reservoir. Three viral lineages closely related to viruses from neighboring countries are currently circulating in Laos. Data provide evidence of periodic historic exchanges of the viruses with neighboring countries, but no recent invasion.     

Pre-cut Filter Paper for Detecting Anti-Japanese Encephalitis Virus IgM from Dried Cerebrospinal Fluid Spots

BackgroundThe use of filter paper as a simple, inexpensive tool for storage and transportation of blood, ‘Dried Blood Spots’ or Guthrie cards, for diagnostic assays is well-established. In contrast, there are a paucity of diagnostic evaluations of dried cerebrospinal fluid (CSF) spots. These have potential applications in low-resource settings, such as Laos, where laboratory facilities for central nervous system (CNS) diagnostics are only available in Vientiane. In Laos, a major cause of CNS infection is Japanese encephalitis virus (JEV). We aimed to develop a dried CSF spot protocol and to evaluate its diagnostic performance using the World Health Organisation recommended anti-JEV IgM antibody capture enzyme-linked immunosorbent assay (JEV MAC-ELISA).Conclusions/SignificanceThe novel design of pre-cut filter paper saturated with CSF could provide a useful tool for JEV diagnostics in settings with limited laboratory access. It has the potential to improve national JEV surveillance and inform vaccination policies. The saturation of filter paper has potential use in the wider context of pathogen detection, including dried spots for detecting other analytes in CSF, and other body fluids.     

Cardiac structural changes and electrical remodeling in a thiamine-deficiency model in rats

AimsThiamine is an important cofactor present in many biochemical reactions, and its deprivation can lead to heart dysfunction. Little is known about the influence of thiamine deprivation on the electrophysiological behavior of the isolated heart cells and information about thiamine deficiency in heart morphology is controversial. Thus, we decided to investigate the major repolarizing conductances and their influence in the action potential (AP) waveform as well as the changes in the heart structure in a set of thiamine deficiency in rats.Main methodsUsing the patch-clamp technique, we investigated inward (I_K1) and outward K⁺ currents (I_to), T-type and L-type Ca²⁺ currents and APs. To evaluate heart morphology we used hematoxylin and eosin in transversal heart sections.Key findingsThiamine deficiency caused a marked decrease in left ventricle thickness, cardiomyocyte number, cell length and width, and membrane capacitance. When evaluating I_to we did not find difference in current amplitude; however an acceleration of I_to inactivation was observed. I_K1 showed a reduction in the amplitude and slope conductance, which implicated a less negative resting membrane potential in cardiac myocytes isolated from thiamine-deficient rats. We did not find any difference in L-type Ca²⁺ current density. T-type Ca²⁺ current was not observed. In addition, we did not observe significant changes in AP repolarization.SignificanceBased on our study we can conclude that thiamine deficiency causes heart hypotrophy and not heart hypertrophy. Moreover, we provided evidence that there is no major electrical remodeling during thiamine deficiency, a feature of heart failure models.     

Household Demography and Early Childhood Mortality in a Rice-Farming Village in Northern Laos

This paper extends Alexandr Chayanov’s model of changing household demography (specifically the ratio of food consumers to food producers) and its influence on agricultural behavior so that it includes possible adverse effects of a rising ratio on nutritional status and early childhood mortality within the household. We apply the model to 35 years’ worth of longitudinal demographic and economic data collected in the irrigated-rice growing village of Na Savang in northern Laos. When appropriate controls are included for other household variables, unobserved inter-household heterogeneity, and changes in local conditions and national policy over the study period, the analysis suggests that a unit increase in the household’s consumer/producer ratio induces something like a nine-fold increase in the risk of death among household members aged less than five years. Monte Carlo simulation studies suggest that this may be an over-estimate but also that the effect is probably real and likely to be an important factor in household demography. At the very least, the results suggest that Chayanov’s model still has theoretical relevance and deserves to be revived.     

Synthesis,physico-chemical properties and effect of adenosine thiamine triphosphate on vitamin B1 metabolism in the liver of alloxan diabetic rats

BackgroundAdenosine thiamine triphosphate (AThTP) is a nucleotide discovered in bacteria and some other living organisms more than a decade ago. No biochemical function for AThTP has been established yet, however, experimental data available indicate its possible involvement in metabolic regulation or cell signaling. Metabolism of AThTP in mammals, as well as the feasibility of its pharmacological application, is essentially unstudied.MethodsPreparative low-pressure chromatography was employed to purify chemically synthesized AThTP with its further analysis by mass spectrometry, HPLC, UV and fluorescence spectroscopy. Enzyme activity assays along with HPLC were used to examine the effects of AThTP and thiamine on vitamin B₁ metabolism in the liver of alloxan-induced diabetic rats.ResultsAn improved procedure for AThTP synthesis and purification is elaborated. Solution stability, optical spectral properties and the molar absorption coefficient for AThTP were determined. The levels of thiamine compounds were found to be increased in the liver of diabetic rats. Neither AThTP nor thiamine treatment affected hepatic vitamin B₁ metabolism. Fasting blood glucose concentration was also unchangeable after AThTP or thiamine administration.General significanceContrast to the widespread view about thiamine deficiency in diabetes, our results clearly shows an adaptive increase in the level of B₁ vitamers in the liver of alloxan diabetic rats with no further rising after AThTP or thiamine treatment at a moderate dose. Neither AThTP nor thiamine is effective in glycaemic control. These findings are to be considered in future studies dealing with thiamine or its analogues application to correct metabolic disturbances in diabetes.     

Patterns and Risks of Trichinella Infection in Humans and Pigs in Northern Laos

Several outbreaks of trichinellosis associated with the consumption of raw pork have occurred in Laos since 2004. This cross-sectional study was conducted in four provinces of northern Laos to investigate the seroepidemiology of trichinellosis in the human population and determine the prevalence and species of Trichinella infection in the domestic pig population. Serum samples and questionnaire data were obtained from 1419 individuals. Serum samples were tested for Trichinella antibodies by ELISA using larval excretory–secretory (ES) antigens and a subset of 68 positive samples were tested by western blot. The seroprevalence of Trichinella antibodies was 19.1% (95% confidence interval (CI) = 17.1–21.1%). The risk of having antibodies detected by ELISA using ES antigens increased with age, being of Lao-Tai ethnicity, living in Oudomxay province and being male. Tongue and diaphragm muscle samples were collected from 728 pigs and tested for Trichinella larvae by the artificial digestion method. Trichinella larvae were isolated from 15 pigs (2.1%) of which 13 were identified as T. spiralis by molecular typing; the species of the two remaining isolates could not be determined due to DNA degradation. Trichinella spp. are endemic in the domestic environment of northern Laos and targeted preventative health measures should be initiated to reduce the risk of further outbreaks occurring.     

Thiamine deficiency in fishes: causes,consequences, and potential solutions

Thiamine deficiency complex (TDC) is a disorder resulting from the inability to acquire or retain thiamine (vitamin B₁) and has been documented in organisms in aquatic ecosystems ranging from the Baltic Sea to the Laurentian Great Lakes. The biological mechanisms leading to TDC emergence may vary among systems, but in fishes, one common outcome is high mortality among early life stages. Here, we review the causes and consequences of thiamine deficiency in fishes and identify potential solutions. First, we examine the biochemical and physiological roles of thiamine in vertebrates and find that thiamine deficiency consistently results in impaired neurological function across diverse taxa. Next, we review natural producers of thiamine, which include bacteria, fungi, and plants, and suggest that thiamine is not currently limiting for most animal species inhabiting natural aquatic environments. A survey of historic occurrences of thiamine deficiency identifies consumption of a thiamine-degrading enzyme, thiaminase, as the primary explanation for low levels of thiamine in individuals and subsequent onset of TDC. Lastly, we review conservation and management strategies for TDC mitigation ranging from evolutionary rescue to managing for a diverse forage base. As recent evidence suggests occurrences of thiamine deficiency may be increasing in frequency, increased awareness and a better mechanistic understanding of the underlying causes associated with thiamine deficiency may help prevent further population declines.     

Effects of thiamine and pyridoxine on respiratory activity in Saccharomyces carlsbergensis strain 4228

Studies were made to elucidate the relationship among the thiamine-induced growth inhibition, decrease in cellular vitamin B₆ content and respiratory deficiency in Saccharomyces carlsbergensis strain 4228 [Nakamura et al., Biochem. Biophys. Res. Commun. 59, 771–776 (1974)]. Addition of pyridoxine to the thiamine-added culture at the beginning or in the course of cultivation brought about appearance of cytochrome spectra and the increase in the activity of heme-containing enzymes and in respiratory activity (Q _{O 2}). The effects of pyridoxine occurred prior to the restoration of growth. Pyridoxine was effective even in the presence of high levels of glucose in the growth medium (not less than 3%). On the basis of these results, the mechanism of the effects of thiamine and pyridoxine was discussed.     

Do the Preferences of Healthcare Provider Selection Vary among Rural and Urban Patients with Different Income and Cause Different Outcome?

BackgroundEqual access to healthcare facilities and high-level quality of care are important strategies to eliminate the disparity in outcome of care. However, the existing literature regarding how urban or rural dwelling patients with different income level select healthcare providers is insufficient. The purposes of this study were to examine whether differences of healthcare provider selection exist among urban and rural coronary artery bypass surgery (CABG) patients with different income level. If so, we further investigated the associated impact on mortality.MethodsA retrospective, multilevel study design was conducted using claims data from 2007–2011 Taiwan’s Universal Health Insurance Scheme. Healthcare providers’ performance and patients’ travelling distance to hospitals were used to define the patterns of healthcare provider selection. Baron and Kenny’s procedures for mediation effect were conducted.ResultsThere were 10,108 CABG surgeries included in this study. The results showed that urban dwelling and higher income patients were prone to receive care from better-performance providers. The travelling distances of urban dwelling patients was 15 KM shorter, especially when they received better-performance provider’s care. The results also showed that the difference of healthcare provider selection and mortality rate existed between rural and urban dwelling patients with different income levels. After the procedure of mediation effect testing, the results showed that the healthcare provider selection partially mediated the relationships between patients’ residential areas with different income levels and 30-day mortality.ConclusionPreferences of healthcare provider selection vary among rural and urban patients with different income, and such differences partially mediated the outcome of care. Health authorities should pay attention to this issue, and propose appropriate solutions to eliminate the disparity in outcome of CABG care.     

Phylogeography and genetic diversity of the widespread katydid Ducetia japonica (Thunberg, 1815) across China

Habitat fragmentation can lower migration rates and genetic connectivity among remaining populations of native species. Ducetia japonica is one of the most widespread katydids in China, but little is known about its genetic structure and phylogeographic distribution. We combined the five‐prime region of cytochrome c oxidase subunit I (COI‐5P), 11 newly developed microsatellite loci coupled with an ecological niche model (ENM) to examine the genetic diversity and population structure of D. japonica in China and beyond to Laos and Singapore. Both Bayesian inference (BI) and haplotype network methods revealed six mitochondrial COI‐5P lineages. The distribution of COI‐5P haplotypes may not demonstrate significant phylogeographic structure (N _ST > G _ST, p > .05). The STRUCTURE analysis based on microsatellite data also revealed six genetic clusters, but discordant with those obtained from COI‐5P haplotypes. For both COI‐5P and microsatellite data, Mantel tests revealed a significant positive correlation between geographic and genetic distances in mainland China. Bayesian skyline plot (BSP) analyses indicated that the population size of D. japonica''s three major mitochondrial COI‐5P lineages were seemingly not affected by last glacial maximum (LGM, 0.015–0.025 Mya). The ecological niche models showed that the current distribution of D. japonica was similar to the species’ distribution during the LGM period and only slightly extended in northern China. Further phylogeographic studies based on more extensive sampling are needed to identify specific locations of glacial refugia in northern China.     

A Four-Way Comparison of Cardiac Function with Normobaric Normoxia,Normobaric Hypoxia,Hypobaric Hypoxia and Genuine High Altitude

BackgroundThere has been considerable debate as to whether different modalities of simulated hypoxia induce similar cardiac responses.ResultsAll 14 subjects completed the experiment at GHA, 11 at NN, 12 under NH, and 6 under HH. The four groups were similar in age, sex and baseline demographics. At baseline rest right ventricular (RV) systolic pressure (RVSP, p = 0.0002), pulmonary vascular resistance (p = 0.0002) and acute mountain sickness (AMS) scores were higher and the SpO₂ lower (p<0.0001) among all three hypoxic groups (GHA, NH and HH) compared with NN. At both 15 minutes and 120 minutes post exercise, AMS scores, Cardiac output, septal S’, lateral S’, tricuspid S’ and A’ velocities and RVSP were higher and SpO₂ lower with all forms of hypoxia compared with NN. On post-test analysis, among the three hypoxia groups, SpO₂ was lower at baseline and 15 minutes post exercise with GHA (89.3±3.4% and 89.3±2.2%) and HH (89.0±3.1 and (89.8±5.0) compared with NH (92.9±1.7 and 93.6±2.5%). The RV Myocardial Performance (Tei) Index and RVSP were significantly higher with HH than NH at 15 and 120 minutes post exercise respectively and tricuspid A’ was higher with GHA compared with NH at 15 minutes post exercise.ConclusionsGHA, NH and HH produce similar cardiac adaptations over short duration rest despite lower SpO₂ levels with GHA and HH compared with NH. Notable differences emerge following exercise in SpO_2, RVSP and RV cardiac function.     

Consistent Condom Use during Casual Sex among Long-Truck Drivers in Togo

BackgroundIn 2008, the proportion of truck drivers who were not systematically protected during sex was 63% with casual partners and 60% with sex workers. Despite the high level of knowledge on HIV/AIDS and the growing awareness of the existence of the risk of HIV infection, condom use always encounters resistance among truck drivers in Togo. We sought to document the factors associated with condom use during casual sex among trucks’ drivers in Togo.MethodsThis was an analytical cross-sectional study conducted in 2010 and targeted truckers at truck station on the two main roads of Togo, Lomé-Cinkassé and Kodjoviakopé-Sanvee Condji.ResultsIn this study, 1,782 trucks’ drivers and their helpers were interviewed. All were men, and their mean age was 28.8 ± 8.8 years. Trucks’ drivers were doing an average of 3 stops on their journeys and 1,229 (69%) of them had at least two years of experience in the work. Of the 1,782 trucks’ drivers, only 620 (34.8%) had consistently used condoms during casual sex in the last three months. In multivariate analysis, predictors were: education level (primary schooling: OR = 1.54; p = 0.002; Secondary schooling and higher OR = 1.38; p = 0.036), good knowledge of ways of HIV transmission (OR = 1.53; p = 0.000), tested for HIV (OR = 1.67, p = 0.000), duration in the profession (2–5 years: OR = 1.43, p = 0.008; more than 5 years: OR = 1.38, p = 0.027), and HIV risk’s perception (OR = 1.44, p = 0.000).ConclusionThese results highlight factors associated with consistent condom use during casual sex by truck drivers in Togo. This is a key population group at high risk of HIV transmission toward which the national HIV/AIDS control program should strengthen the HIV prevention strategies.     

Preliminary Results of National Amyotrophic Lateral Sclerosis (ALS) Registry Risk Factor Survey Data

BackgroundThe National ALS Registry is made up of two components to capture amyotrophic lateral sclerosis (ALS) cases: national administrative databases (Medicare, Medicaid, Veterans Health Administration and Veterans Benefits Administration) and self-identified cases captured by the Registry’s web portal. This study describes self-reported characteristics of U.S. adults with ALS using the data collected by the National ALS Registry web portal risk factor surveys only from October 19, 2010 through December 31, 2013.ObjectiveTo describe findings from the National ALS Registry’s web portal risk factor surveys.MeasurementsThe prevalence of select risk factors among adults with ALS was determined by calculating the frequencies of select risk factors—smoking and alcohol (non, current and former) histories, military service and occupational history, and family history of neurodegenerative diseases such as ALS, Alzheimer’s and/or Parkinson’s.ResultsNearly half of survey respondents were ever smokers compared with nearly 41% of adults nationally. Most respondents were ever drinkers which is comparable to national estimates. The majority were light drinkers. Nearly one-quarter of survey respondents were veterans compared with roughly 9% of US adults nationally. Most respondents were retired or disabled. The industries in which respondents were employed for the longest time were Professional and Scientific and Technical Services. When family history of neurodegenerative diseases in first degree relatives was evaluated against our comparison group, the rates of ALS were similar, but were higher for Parkinson’s disease, Alzheimer’s disease and any neurodegenerative diseases.ConclusionsThe National ALS Registry web portal, to our knowledge, is the largest, most geographically diverse collection of risk factor data about adults living with ALS. Various characteristics were consistent with other published studies on ALS risk factors and will allow researchers to generate hypotheses for future research.     

Vocal Diversity and Taxonomy of <Emphasis Type="Italic">Nomascus</Emphasis> in Central Vietnam and Southern Laos

Previous researchers suggested that gibbon song repertoire is genetically determined and song characteristics are useful for assessing systematic relationships. The southern white-cheeked crested gibbon is regarded as either a subspecies of Nomascus leucogenys or its own species (Nomascus siki). I studied vocal diversity among different wild populations of Nomascus in central Vietnam and southern Laos to assess their taxonomic relationships and to examine whether their vocal patterns correspond to forms previously described for Nomascus siki. I examined the songs of 7 Nomascus populations in Vietnam and Laos. I analyzed 192 song bouts from different gibbon groups including 173 phrases of 42 females and 192 phrases of 42 males. Linear discriminant analysis, classification trees, and multidimensional scaling revealed marked separation of groups in the northern and southern populations. Within the 2 geographic populations, there is little variability and the vocal characteristics exhibited no apparent cline. I conclude that the northern and southern geographic populations may represent 2 distinct taxa. I postulate that a taxonal boundary such as large rivers existing between southern Quang Binh province and northern Thua-Thien Hue province in Vietnam and northern Phou Xang He NBCA and southern Dong Phou Vieng NBCA in Laos has limited gene flow between the populations. Differing topographic features could also serve as a selective force for improved sound transmission in a highly territorial species, driving the divergence between the 2 populations.     

Multigene Phylogeography of Bactrocera caudata (Insecta: Tephritidae): Distinct Genetic Lineages in Northern and Southern Hemispheres

Bactrocera caudata is a pest of pumpkin flower. Specimens of B. caudata from the northern hemisphere (mainland Asia) and southern hemisphere (Indonesia) were analysed using the partial DNA sequences of the nuclear 28S rRNA and internal transcribed spacer region 2 (ITS-2) genes, and the mitochondrial cytochrome c oxidase subunit I (COI), cytochrome c oxidase subunit II (COII) and 16S rRNA genes. The COI, COII, 16S rDNA and concatenated COI+COII+16S and COI+COII+16S+28S+ITS-2 nucleotide sequences revealed that B. caudata from the northern hemisphere (Peninsular Malaysia, East Malaysia, Thailand) was distinctly different from the southern hemisphere (Indonesia: Java, Bali and Lombok), without common haplotype between them. Phylogenetic analysis revealed two distinct clades (northern and southern hemispheres), indicating distinct genetic lineage. The uncorrected ‘p’ distance for the concatenated COI+COII+16S nucleotide sequences between the taxa from the northern and southern hemispheres (‘p’ = 4.46-4.94%) was several folds higher than the ‘p’ distance for the taxa in the northern hemisphere (‘p’ = 0.00-0.77%) and the southern hemisphere (‘p’ = 0.00%). This distinct difference was also reflected by concatenated COI+COII+16S+28S+ITS-2 nucleotide sequences with an uncorrected ''p'' distance of 2.34-2.69% between the taxa of northern and southern hemispheres. In accordance with the type locality the Indonesian taxa belong to the nominal species. Thus the taxa from the northern hemisphere, if they were to constitute a cryptic species of the B. caudata species complex based on molecular data, need to be formally described as a new species. The Thailand and Malaysian B. caudata populations in the northern hemisphere showed distinct genetic structure and phylogeographic pattern.     

The Current Impact of Incidental Findings Found during Neuroimaging on Neurologists’ Workloads

ObjectiveNeuroimaging is an important diagnostic tool in the assessment of neurological disease, but often unmasks Incidental Findings (IFs). The negative impacts of IFs, such as ‘patient’ anxiety, present neurologists with management dilemmas, largely due to the limited knowledge base surrounding the medical significance of these IFs. In particular, the lack of evidence-based clinical trials investigating the efficacy of treatments for subclinical IFs makes management protocols challenging. The objective was to determine the impact IFs may have on neurologists’ workloads and healthcare budgets and to examine neurologists’ concerns regarding the clinical management of these ‘patients’.MethodsQualitative research based on constructivist grounded theory. Data was collected through semi-structured interviews of purposively sampled neurologists, coded, and concurrent comparative analysis performed. A substantive theory of the ‘IF impacts’ was developed after concept saturation.ResultsNeurologists managed the escalating workload caused by an increased number of referrals of ‘patients’ with IFs found during neuroimaging; however it was unclear whether this was sustainable in the future. Neurologists experienced IF management dilemmas and spent more time with ‘patients’ affected by anxiety. The lack of information provided to those undergoing neuroimaging by the referring clinician regarding the possibility of discovering IFs was highlighted.ConclusionThe impact of IFs upon the neurologist, ‘patient’ and the health institution appeared considerable. Further research determining the natural history of subclinical IFs and the efficacy of intervention will help to alleviate these issues.     

Thiamine deficiency in rats affects thiamine metabolism possibly through the formation of oxidized thiamine pyrophosphate

BackgroundThiamine deficiency (TD) has a number of features in common with the neurodegenerative diseases development and close relationship between TD and oxidative stress (OS) has been repeatedly reported in the literature. The aim of this study is to understand how alimentary TD, accompanied by OS, affects the expression and level of two thiamine metabolism proteins in rat brain, namely, thiamine transporter 1 (THTR1) and thiamine pyrophosphokinase (TPK1), and what factors are responsible for the observed changes.MethodsThe effects of OS caused by TD on the THTR1and TPK1 expression in rat cortex, cerebellum and hippocampus were examined. The levels of active and oxidized forms of ThDP (enzymatically measured) in the blood and brain, ROS and SH-groups in the brain were also analyzed.ResultsTD increased the expression of THTR1 and protein level in all studied regions. In contrast, expression of TPK1 was depressed. TD-induced OS led to the accumulation of ThDP oxidized inactive form (ThDP_ox) in the blood and brain. In vitro reduction of ThDP_ox by dithiothreitol regenerates active ThDP suggesting that ThDP_ox is in disulfide form. A single high-dose thiamine administration to TD animals had no effect on THTR1 expression, partly raised TPK1 mRNA and protein levels, but is unable to normalize TPK1 enzyme activity. Brain and blood ThDP levels were increased in these conditions, but ThDP_ox was not decreased.General significanceIt is likely, that the accumulation of ThDP_ox in tissue could be seen as a potential marker of neurocellular dysfunction and thiamine metabolic state.     

Sex-chromosome differentiation and ‘sex races’ in the common frog (Rana temporaria)

Sex-chromosome differentiation was recently shown to vary among common frog populations in Fennoscandia, suggesting a trend of increased differentiation with latitude. By rearing families from two contrasted populations (respectively, from northern and southern Sweden), we show this disparity to stem from differences in sex-determination mechanisms rather than in XY-recombination patterns. Offspring from the northern population display equal sex ratios at metamorphosis, with phenotypic sexes that correlate strongly with paternal LG₂ haplotypes (the sex chromosome); accordingly, Y haplotypes are markedly differentiated, with male-specific alleles and depressed diversity testifying to their smaller effective population size. In the southern population, by contrast, a majority of juveniles present ovaries at metamorphosis; only later in development do sex ratios return to equilibrium. Even at these later stages, phenotypic sexes correlate only mildly with paternal LG₂ haplotypes; accordingly, there are no recognizable Y haplotypes. These distinct patterns of gonadal development fit the concept of ‘sex races’ proposed in the 1930s, with our two populations assigned to the ‘differentiated’ and ‘semi-differentiated’ races, respectively. Our results support the suggestion that ‘sex races’ differ in the genetic versus epigenetic components of sex determination. Analysing populations from the ‘undifferentiated race’ with high-density genetic maps should help to further test this hypothesis.